1. Field of the Invention
The present invention concerns a self-tapping screw, especially for wood-plastic composite materials or the like, including a screw head, an adjacent screw shaft and a screw tip, where two threaded sections have been formed on the screw shaft, the two threaded sections being separated by a thread-free section, and where each of the threads of the two threaded sections has a different pitch.
2. Description of Related Art
The German patent to Gebrauchsmuster 200 07 321.4 discloses a screw of the kind described above. This design of a screw leads to the result, that when two adjacent fasteners are to be joined by means of screws, they can be screwed together without pre-drilling in such a manner that the absence of a gap between the two fasteners can be ensured and an initial tensioning force can be generated. For this purpose, the two threaded sections contain threads with different pitches, where the threaded section closest to the screw tip has a greater pitch than the other threaded section. Similar screws are also shown in GB-PS 2 169 051, WO 99/15796, and EP 0 460 264 A1.
When the known screws are threaded into wood-plastic-composite materials, it has been found that an increased production of chips occurs, while the chips are transported away from the upper threaded portion the chips are thrown up below the screw head.